This research focuses on oxidative modification of proteins. The resulting covalent modifications have been implicated in important physiologic and pathologic processes. Determination of the actual roles of oxidative modification in these processes requires the identification of specific proteins which are susceptible to modification and the mapping of the sites of modification in those proteins. During this year, we continued to focus on the physiological functions of oxidative modification of proteins. The modifications being studied in most detail are those of cysteine oxidation of iron-responsive protein-2 and methionine oxidation of glutamine synthetase. Iron-responsive protein-2 is a 100 kD protein which binds to mRNA targets, altering both translation efficiency and RNA stability. We have now shown that a 7 kD region of the protein binds iron with high affinity. The iron-bound peptide then mediates an oxygen-dependent modification which oxidizes a single cysteine residue. Thus, this small section of the protein serves as an efficient iron sensor and can regulate the cellular content of the iron-responsive protein-2, because the oxidatively modified protein can be degraded by the proteasome. We showed previously that the mouse model of the neurodegenerative disease ataxia-telangiectasia, ATM, is characterized by oxidative stress and oxidative modification of macromolecules. This year we completed two collaborative studies which tested the ability of antioxidants to reduce oxidative damage and to correct the neurobehavioral abnormality in this mouse model.